Underwater wireless communication via TENG-generated Maxwell's displacement current

Improving the Operational Stability of the Sb2Se3-Based Self-Powered Photodetector via Interfacial Engineering

Originating from photovoltaic devices, self-powered photodetectors (SPPDs) have low power consumption and show promising applications in photoelectric imaging and optical communications. Many efforts have been devoted to improving their photodetection performances, including responsivity, detectivity, and response time. However, work on their operational stability, one of the key parameters of applied PDs, is still rare. Here, using an interfacial engineering method, we improve the operational stability of the representative Sb2Se3-based SPPD. The Sb2O3 modification layer is applied at the interface between the Sb2Se3 and TiO2 layers and characterized systematically. With the optimized fabrication of the Sb2O3 layer, the operational stability under both air ambient and underwater conditions is significantly enhanced. Moreover, the performances of the SPPD, including responsivity, detectivity, and response time, are improved to 0.45 A/W, 2.70 × 1013 Jones, and 81.5/75.0 ns, respectively. Specifically, without encapsulation, the photoresponse and key photodetection parameters of the devices vary by only around ten percent after working underwater. Our work provides a facile and effective way to modify the interfacial properties of the Sb2Se3 heterostructure and improve the operational stability of the SPPD.

3D Printing of Auxetic Self-powered Mechanoluminescent Photonic Skins for Underwater Communication and Safety Monitoring

Stretchable mechanoluminescent (ML) photonic skin with strong and stable brightness holds great promise for underwater communication and safety monitoring. However, traditional film-based ML devices often lack the compliance needed to accommodate curved surfaces and face a trade-off between extensibility and luminescent intensity. This study introduces a 3D-printed self-powered auxetic ML photonic skin. By utilizing auxetic materials with a negative Poisson's ratio, we created a stretchable ML device that conforms to complex, curved surfaces, enhancing its applicability in dynamic underwater settings. By encapsulating the auxetic ML structure in silicone, simultaneous improvements in brightness uniformity and stretchability are achieved. The device exhibits remarkable durability, maintaining consistent light emission and mechanical performance over 10 000 cycles, and demonstrates the potential for real-time underwater communication and safety monitoring. Integrated into a glove, a swimming toy, and a gas tank, the photonic skin successfully transmitted Morse code signals and detected gas leaks, showcasing its versatility and robustness in harsh underwater conditions. These findings underscore the potential of this technology to improve safety and efficiency in marine exploration, paving the way for further advancements in underwater robotics and communication.

A wearable, ultrasonically-actuated magnetic-dipole rotating resonator for mobile communication in cross-medium environment

Traditional MHz and GHz electromagnetic antennas face challenges of high attenuation rate in cross-medium communication; while mechanical antennas are hindered by their large size, high energy consumption and weak radiation capacity. Here, we report a centimeter-scale, wearable ultrasonically-actuated magnetic-dipole rotating resonator (UA-MDRR) for efficient extremely low frequency (ELF) electromagnetic wave transmission in extreme environments. The UA-MDRR employs a small multilayer piezoelectric ceramic (0.11 cm³) to rotate a disc-type NdFeB magnet, generating ELF radiation through an electro-mechanical-magnetic (EMM) coupling effect. This device achieves a high emission capacity of 24,000 nT/cm³@1 m, outperforming the state-of-the-art resonators/antennas by one to two orders of magnitude. It can emit a magnetic field strength of 2.64 pT in air and 2.12 pT underwater at 100 m, respectively, while consuming only 0.61 W of power. This innovation represents a groundbreaking advancement in cross-medium communication, offering a mobile wearable device for emergency communication in seawater for life saving.

Self-Powered and Self-Healing Underwater Sensors with Functions of Intelligent Drowning Warning and Rescuing by Using a Nonswelling Hydrogel

Hydrogels have attracted increasing attention in wearable sensors, but preparing underwater hydrogel sensors with excellent anti-swelling and self-healing properties is still challenging. Herein, an anti-swelling and self-healing hydrogel is prepared by grafting poly(acrylic acid) with hydrophobic lauryl methacrylate, as well as constructing a second network and multiple molecular interactions (abbreviated as PALCF). The introduced hydrophobic long alkyl chains and the increased cross-linking density of the hydrogel result in a swelling ratio of only 0.04% after immersion in water for 15 days. Due to abundant metal coordination and hydrogen bonds, the PALCF hydrogel exhibits a high tensile stress of 0.60 MPa and a self-healing efficiency reaching 96.0% after self-healing at 60 °C for 2 min. Based on the piezoresistive effect, the PALCF hydrogel is directly used as an underwater strain sensor with a high sensitivity (GF = 2.24) to control underwater vehicles for rescue implementation. Furthermore, two self-powered triboelectric nanogenerator sensors with contact and non-contact models are constructed based on PALCF hydrogels for underwater communication, capable of sending out SOS messages and drowning alarms in emergency. The proposed underwater sensors with drowning warning and rescuing functions have the potential for use in drowning prevention, human-machine interfaces, and underwater communication system.

Maximizing Output Energy via Suppressing Charge Loss and Increasing Load Voltage in Charge Extraction Process

The effective collection of interfacial tribo-charges and an increase in load voltage are two essential factors that improve the output energy of triboelectric nanogenerators. However, some tribo-charges are hardly collected through one or multiple integrated side electrodes based on corona discharge, and their load voltages are limited by air breakdown in adjacent electrodes. In this study, a dynamic quasi-dipole potential distribution model is proposed to systematically reveal the mechanisms of interfacial tribo-charge loss. Based on this model, an optimization route is designed to reduce the interfacial charge loss stepwise, achieving a 15-fold improvement in charge collection from the tribo-interface. A potential difference enhancement strategy is used for the first time to increase the air breakdown threshold between the inner electrodes and increase the output voltage under a large load. By effective increase in charge collection efficiency and load voltage, a historical record output energy density of 5.03 J m-2 is obtained. This study refined and optimized the interfacial charge loss mechanisms and provided advanced guidance for efficiently extracting energy during the triboelectrification process.

Highly Stretchable Conductive Hydrogel-Based Flexible Triboelectric Nanogenerators for Ultrasensitive Tactile Sensing

Wearable electronic devices have shown great application prospects in the fields of tactile sensing, electronic skin, and soft robots. However, the existing wearable electronic devices face limitations such as power supply challenges, lack of portability, and discomfort, which restrict their applications. The invention of triboelectric nanogenerators (TENGs) with dual functions of energy harvesting and sensing provides an innovative solution to address these issues. This study prepared a highly stretchable conductive hydrogel using doped conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) as a strain sensor, demonstrating high sensitivity (GF = 4.31), an ultra-wide sensing range (0-1690%), ultra-fast response speed (0.15 s), excellent durability, and repeatability. A high-performance triboelectric nanogenerator was constructed using the hydrogel as an electrode, achieving an output performance of up to 192 V. Furthermore, the TENG fixed in the hands, wrists, legs, and feet of the human body can be used as a wearable electronic device to monitor human motion, which is conducive to promoting the development of triboelectric nanogenerators based on conductive hydrogels in strain sensors and self-powered wearable devices.

Advanced Dielectric Materials for Triboelectric Nanogenerators: Principles, Methods, and Applications

Triboelectric nanogenerator (TENG) manifests distinct advantages such as multiple structural selectivity, diverse selection of materials, environmental adaptability, low cost, and remarkable conversion efficiency, which becomes a promising technology for micro-nano energy harvesting and self-powered sensing. Tribo-dielectric materials are the fundamental and core components for high-performance TENGs. In particular, the charge generation, dissipation, storage, migration of the dielectrics, and dynamic equilibrium behaviors determine the overall performance. Herein, a comprehensive summary is presented to elucidate the dielectric charge transport mechanism and tribo-dielectric material modification principle toward high-performance TENGs. The contact electrification and charge transport mechanism of dielectric materials is started first, followed by introducing the basic principle and dielectric materials of TENGs. Subsequently, modification mechanisms and strategies for high-performance tribo-dielectric materials are highlighted regarding physical/chemical, surface/bulk, dielectric coupling, and structure optimization. Furthermore, representative applications of dielectric materials based TENGs as power sources, self-powered sensors are demonstrated. The existing challenges and promising potential opportunities for advanced tribo-dielectric materials are outlined, guiding the design, fabrication, and applications of tribo-dielectric materials.

Triboelectric Nanogenerator for Self-Powered Gas Sensing

With the continuous acceleration of industrialization, gas sensors are evolving to become portable, wearable and environmentally friendly. However, traditional gas sensors rely on external power supply, which severely limits their applications in various industries. As an innovative and environmentally adaptable power generation technology, triboelectric nanogenerators (TENGs) can be integrated with gas sensors to leverage the benefits of both technologies for efficient and environmentally friendly self-powered gas sensing. This paper delves into the basic principles and current research frontiers of the TENG-based self-powered gas sensor, focusing particularly on innovative applications in environmental safety monitoring, healthcare, as well as emerging fields such as food safety assurance and smart agriculture. It emphasizes the significant advantages of TENG-based self-powered gas sensor systems in promoting environmental sustainability, achieving efficient sensing at room temperature, and driving technological innovations in wearable devices. It also objectively analyzes the technical challenges, including issues related to performance enhancement, theoretical refinement, and application expansion, and provides targeted strategies and future research directions aimed at paving the way for continuous progress and widespread applications in the field of self-powered gas sensors.

Charge Generation and Enhancement of Key Components of Triboelectric Nanogenerators: A Review

The past decade has witnessed remarkable progress in high-performance Triboelectric nanogenerators (TENG) with the design and synthesis of functional dielectric materials, the exploration of novel dynamic charge transport mechanisms, and the innovative design of architecture, making it one of the most crucial technologies for energy harvesting. High output charge density is fundamental for TENG to expand its application scope and accelerate industrialization; it depends on the dynamic equilibrium of charge generation, trapping, de-trapping, and migration within its core components. Here, this review classifies and summarizes innovative approaches to enhance the charge density of the charge generation, charge trapping, and charge collection layers. The milestone of high charge density TENG is reviewed based on material selection and innovative mechanisms. The state-of-the-art principles and techniques for generating high charge density and suppressing charge decay are discussed and highlighted in detail, and the distinct charge transport mechanisms, the technologies of advanced materials preparation, and the effective charge excitation strategy are emphatically introduced. Lastly, the bottleneck and future research priorities for boosting the output charge density are summarized. A summary of these cutting-edge developments intends to provide readers with a deep understanding of the future design of high-output TENG.

Octopus-Inspired Underwater Soft Robotic Gripper with Crawling and Swimming Capabilities

Can a robotic gripper only operate when attached to a robotic arm? The application space of the traditional gripper is limited by the robotic arm. Giving robot grippers the ability to move will expand their range of applications. Inspired by rich behavioral repertoire observed in octopus, we implement an integrated multifunctional soft robotic gripper with 6 independently controlled Arms. It can execute 8 different gripping actions for different objects, such as irregular rigid/soft objects, elongated objects with arbitrary orientation, and plane/curved objects with larger sizes than the grippers. Moreover, the soft gripper can realize omnidirectional crawling and swimming by itself. The soft gripper can perform highly integrated tasks of releasing, crawling, swimming, grasping, and retrieving objects in a confined underwater environment. Experimental results demonstrate that the integrated capabilities of multimodal adaptive grasping and omnidirectional motions enable dexterous manipulations that traditional robotic arms cannot achieve. The soft gripper may apply to highly integrated and labor-intensive tasks in unstructured underwater environments, including ocean litter collecting, capture fishery, and archeological exploration.

A Flexible, Adaptive, and Self-Powered Triboelectric Vibration Sensor with Conductive Sponge-Silicone for Machinery Condition Monitoring

Vibration sensors for continuous and reliable condition monitoring of mechanical equipment, especially detection points of curved surfaces, remain a great challenge and are highly desired. Herein, a highly flexible and adaptive triboelectric vibration sensor for high-fidelity and continuous monitoring of mechanical vibration conditions is proposed. The sensor is entirely composed of flexible materials. It consists of a conductive sponge-silicone layer and a fluorinated ethylene propylene film. It can detect vibration acceleration of 5 to 50 m s-2 and vibration frequency of 10 to 100 Hz. It has strong robustness and stability, and the output performance barely changes after the durability test of 168 000 working cycles. Additionally, the flexible sensor can work even when the detection point of the mechanical equipment is curved, and the linear fit of the output voltage and acceleration is very close to that when the detection point is flat. Finally, it can be applied to monitoring the working condition of blower and vehicle engine, and can transmit vibration signal to mobile phone application through Wi-Fi module for real-time monitoring. The flexible triboelectric vibration sensor is expected to provide a practical paradigm for smart, green, and sustainable wireless sensor system in the era of Internet of Things.

Innovative Synthesis of Zeolitic Imidazolate Framework by a Stovetop Kitchen Pressure Cook Pot for Triboelectric Nanogenerator

This study presents a novel approach utilizing solvothermal techniques to synthesize zeolitic imidazolate framework (ZIF‐4) particles. Various properties of the ZIF‐4 particles are investigated to shed light on the structural and morphological characteristics. These ZIF‐4 particles act as a positive triboelectric layer in the fabrication of a triboelectric nanogenerator (TENG) designed for powering electronic devices. The solvothermal‐assisted synthesis ensures the controlled and efficient production of ZIF‐4, optimizing its characteristics for enhanced performance in the TENG. The generated TENG, based on ZIF‐4 particles, determines promising capabilities in converting mechanical energy into electrical power. The highest power of TENG is obtained to be 18 μW at a load resistance of 50 MΩ. This work contributes major insights to the search for sustainable and effective power solutions for electronic gadgets. It emphasizes the potential of ZIF‐4 as a crucial triboelectric material, demonstrating its importance in the advancement of TENGs.

Nanocomposite Electret Layer Improved Long-Term Stable Solid-Liquid Contact Triboelectric Nanogenerator for Water Wave Energy Harvesting

With the continuous rise of environmental pollution and energy crisis, the global energy revolution is risen. Development of renewable blue energy based on the emerging promising triboelectric nanogenerators (TENG) has become an important direction of future energy development. The solid-liquid contact triboelectric nanogenerator (TENG) has the advantages of flexible structure, easy manufacture, and long-term stability, which makes it easier to integrate and achieve large-scale conversion of wave mechanical energy. However, the electric power output is still not large enough, which limits its practical applications. In this work, a nanocomposite electret layer enhanced solid-liquid contact triboelectric nanogenerator (E-TENG) is proposed for water wave energy harvesting, which can effectively improve the electric output and achieve real-time power supply of wireless sensing. Through introducing a nanocomposite electret layer into flexible multilayer solid-liquid contact TENG, higher power output is achieved. The E-TENG (active size of 50 mm × 49 mm) shows desired output performance, a power density of 521 mW m-2. The generated electric energy can drive wireless temperature sensing by transmitting wireless signals carrying detection information at the period of ˂5.5 min. This research greatly improves the electric output and provides a solid basis for the industrialization of TENG in blue energy.

Underwater Biomimetic Lateral Line Sensor Based on Triboelectric Nanogenerator for Dynamic Pressure Monitoring and Trajectory Perception

Developing desirable sensors is crucial for underwater perceptions and operations. The perceiving organs of marine creatures have greatly evolved to react accurately and promptly underwater. Inspired by the fish lateral line, this study proposes a triboelectric dynamic pressure sensor for underwater perception. The biomimetic lateral line sensor (BLLS) has high sensitivity to the disturbance amplitude/frequency, good adaptability to underwater environments and (relative) low cost. The sensors are deployed at the bottom of the test basin to perceive various moving objects, such as a robotic fish, robotic seal, etc. By analyzing the electrical signal of the sensor, the motion parameters of the objects passed over can be obtained. By monitoring signal variations across multiple sensors, the ability to sense different disturbance movement trajectories, including linear and angular trajectories, is achievable. The study will prove significant in forming an unconventional underwater perceiving method, which can back-up the sonic/optical sensors when are impaired in complex underwater environments.

All-light communication network for space-air-sea integrated interconnection

Space-air-sea communication networks are of great interest to meet the demand for close and seamless connections between space, land, and ocean environments. Wireless light communication can expand network coverage from land to the sky and even the ocean while offering enhanced anti-interference capabilities. Here, we propose and establish an all-light communication network (ALCN) for space-air-sea integrated interconnection, which merges underwater blue light communication, wireless white light communication, solar-blind deep ultraviolet light communication and laser diode-based space communication. Ethernet switches and the Transmission Control Protocol are used for space-air-sea light interconnection. Experimental results show that the ALCN supports wired and wireless device access simultaneously. Bidirectional data transmission between network nodes is demonstrated, with a maximum packet loss ratio of 5.80% and a transmission delay below 74 ms. The proposed ALCN provides a promising scheme for future space-air-sea interconnections towards multiterminal, multiservice applications.

Implementation of Underwater Electric Field Communication Based on Direct Sequence Spread Spectrum (DSSS) and Binary Phase Shift Keying (BPSK) Modulation

Stable communication technologies in complex waters are a prerequisite for underwater operations. Underwater acoustic communication is susceptible to multipath interference, while underwater optical communication is susceptible to environmental impact. The underwater electric field communication established based on the weak electric fish perception mechanism is not susceptible to environmental interference, and the communication is stable. It is a new type of underwater communication technology. To address issues like short communication distances and high bit error rates in existing underwater electric field communication systems, this study focuses on underwater electric field communication systems based on direct sequence spread spectrum (DSSS) and binary phase shift keying (BPSK) modulation techniques. To verify the feasibility of the established spread spectrum electric field communication system, static communication experiments were carried out in a swimming pool using the DSSS-based system. The experimental results show that in fresh water with a conductivity of 739 μS/cm, the system can achieve underwater current electric field communication within a 11.2 m range with 10-6 bit errors. This paper validates the feasibility of DSSS BPSK in short-range underwater communication, and compact communication devices are expected to be deployed on underwater robots for underwater operations.

Energy Harvesters and Self-Powered Sensors for Smart Electronics, 2nd Edition

With the worldwide rollout of the 5G communication network and 6G around the corner, we have witnessed the rapid development of the Internet of Things (IoT) technology, enabling big data and digital transformation in various fields [...].

A High-Q Electric-Mechano-Magnetic Coupled Resonator for ELF/SLF Cross-Medium Magnetic Communication

Extremely/super low frequency (ELF/SLF) electromagnetic wave can effectively propagate in the harsh cross-medium environment where a high-frequency electromagnetic wave cannot pass due to the fast decay. For efficiently transmitting a strong ELF/SLF radiation signal, the traditional electromagnetic antenna requires a super-large loop (>10 km). To address this issue, in this work, a piezoelectric ceramic/ferromagnetic heterogeneous structured, cantilever beam-type electric-mechano-magnetic coupled resonator at only centimeter scale for ELF/SLF cross-medium magnetic communication is reported. Through designing hard-soft hybrid step-stiffness elastic beam, the resonator exhibits a much higher quality factor Q (≈240) for ELF/SLF magnetic field transmitting, which is one to five orders of magnitude higher than those of previously reported mechanical antennas and loop coil antennas. Moreover, the resonator exhibits a 5000 times higher magnetic field emitting efficiency compared to a conventional loop coil antenna in ELF/SLF band. It also demonstrates a 200% increase in magnetic field emitting capacity compared to existing piezoelectric-driven antennas. In addition, an ASK+PSK modulation method is proposed for suppressing relaxation time of the resonator, and a reduction in the relaxation time by 80% is observed. Furthermore, an air-seawater cross-medium magnetic field communication is successful demonstrated, indicating its potential as portable, high-efficient antenna for underwater and underground communications.

Conformable Multifunctional Space Fabric by Metal 3D Printing for Collision Hazard Protection and Self-Powered Monitoring

The monitoring of space debris assumes paramount significance to ensure the sustainability and security of space activities as well as underground bases in outer space. However, designing a wide range monitoring system with easy fabrication, low power, and high precision remains an urgent challenge under the scarcity of materials and extreme environment conditions of outer space. Here, we designed a one-piece, robust, but flexible, and repairable 3D metal-printed triboelectric nanogenerator (FR-TENG) by incorporating the advantages of standardization and customization of outer space 3D metal printing. Inspired by the structure of hexagonal and pangolin scales, a curved structure is ingeniously applied in the design of 3D printed metal to adapt different curved surfaces while maintaining superior compressive strength, providing excellent flexibility and shape adaptability. Benefiting from the unique structural design, the FR-TENG has a minimum length of 1 cm with a weight of only 3.5 g and the minimum weight resolution detected of 9.6 g, with a response time of 20 ms. Furthermore, a multichannel self-powered collision monitoring system has been developed to monitor minor collisions, providing warnings to determine potential impacts on the space station and bases surfaces. The system may contribute to ensuring the successful completion of space missions and providing a safer space environment for the exploration of extraterrestrial life and the establishment of underground protective bases.

U-Shaped Tube Based Liquid-Solid Triboelectric Nanogenerator for Harvesting Unutilized Compressed Air Energy

Due to a lack of technologies that harvest green and sustainable energy, unutilized compressed air energy during the operation of pneumatic systems is wasted. Liquid-solid triboelectric nano-generators (L-S TENGs) have been widely used as an advanced technology with broad development prospects due to their advantages of a simple structure and long service life. Among them, liquid-solid triboelectric nanogenerators with tube structures have great potential for coupling multiple physical effects and integrating them into a single device. Herein, a U-shaped tube triboelectric nanogenerator composed of fluorinated ethylene propylene (FEP) and copper foil (UFC-TENG) is proposed to directly harvest unutilized compressed air energy. The UFC-TENG can collect unutilized compressed air energy with a stable peak voltage and current of approximately 33 V and 0.25 μA, respectively. When the alternating frequency of the liquid is 0.9 Hz, the unutilized compressed air can drive the UFC-TENG unit with an inner diameter of 12 mm, achieving a maximum output power of 3.93 μW at an external load resistance of 90 MΩ. The UFC-TENG is a novel driving method for L-S TENGs and demonstrates the promising potential of TENGs in the harvesting of unutilized compressed air energy in pneumatic systems.

Boosting Output Performance of Sliding Mode Triboelectric Nanogenerator by Shielding Layer and Shrouded-Tribo-Area Optimized Ternary Electrification Layered Architecture

Sliding mode triboelectric nanogenerator (S-TENG) is effective for low-frequency mechanical energy harvesting owing to their more efficient mechanical energy extraction capability and easy packaging. Ternary electrification layered (TEL) architecture is proven useful for improving the output performance of S-TENG. However, the bottleneck of electric output is the air breakdown on the interface of tribo-layers, which seriously restricts its further improvement. Herein, a strategy is adopted by designing a shielding layer to prevent air breakdown on the central surface of tribo-layers. And the negative effects of air breakdown on the edge of sliding layer are averted by increasing the shrouded area of tribo-layers on slider. Output charge of this shielding-layer and shrouded-tribo-area optimized ternary electrification layered triboelectric nanogenerator (SS-TEL-TENG) achieves 3.59-fold enhancement of traditional S-TENG and 1.76-fold enhancement of TEL-TENG. Furthermore, even at a very low speed of 30 rpm, output charge, current, and average power of the rotation-type SS-TEL-TENG reach 4.15 µC, 74.9 µA, and 25.4 mW (2.05 W m-2 Hz-1 ), respectively. With such high-power output, 4248 LEDs can be lighted brightly by SS-TEL-TENG directly. The high-performance SS-TEL-TENG demonstrated in this work will have great applications for powering ubiquitous sensor network in the Internet of Things (IoT).

Superlensing enables radio communication and imaging underwater

Wireless radio communications provide a backbone to our technological civilization. However, radio communications are widely believed to be impossible in many situations where radios are surrounded by conductive media, such as underwater or underground, thus making ocean exploration difficult and creating well-known mine safety problems. In addition, since most imaging techniques rely on electromagnetic waves, the difficulty of electromagnetic wave propagation through biological tissues, which are mostly made of water, also severely limits bioimaging. Here we show that contrary to common beliefs, radio signals may be efficiently propagated through water over useful distances. Both radio communication and radio imaging through water may be enabled by superlensing of surface electromagnetic waves propagating along the water surface. We have demonstrated underwater radio communication over distances of several hundred skin depth in the MHz frequency range, which would require sensitivity below 10-100 W in a conventional radio communication channel. We also demonstrated subwavelength super-resolution radio imaging in the GHz range by using water surface as a superlens. Our results indicate new ways to perform bioimaging, as well as marine life safe techniques of wireless radio communication and imaging underwater, which are essential for ocean and seafloor exploration. We also anticipate that the developed techniques will provide invaluable means of studying the extraterrestrial water worlds, such as potentially inhabitable Jovian moons.

A Broad Range Triboelectric Stiffness Sensor for Variable Inclusions Recognition

With the development of artificial intelligence, stiffness sensors are extensively utilized in various fields, and their integration with robots for automated palpation has gained significant attention. This study presents a broad range self-powered stiffness sensor based on the triboelectric nanogenerator (Stiff-TENG) for variable inclusions in soft objects detection. The Stiff-TENG employs a stacked structure comprising an indium tin oxide film, an elastic sponge, a fluorinated ethylene propylene film with a conductive ink electrode, and two acrylic pieces with a shielding layer. Through the decoupling method, the Stiff-TENG achieves stiffness detection of objects within 1.0 s. The output performance and characteristics of the TENG for different stiffness objects under 4 mm displacement are analyzed. The Stiff-TENG is successfully used to detect the heterogeneous stiffness structures, enabling effective recognition of variable inclusions in soft object, reaching a recognition accuracy of 99.7%. Furthermore, its adaptability makes it well-suited for the detection of pathological conditions within the human body, as pathological tissues often exhibit changes in the stiffness of internal organs. This research highlights the innovative applications of TENG and thereby showcases its immense potential in healthcare applications such as palpation which assesses pathological conditions based on organ stiffness.

Recent Progress of Advanced Materials for Triboelectric Nanogenerators

Triboelectric nanogenerators (TENGs) have received intense attention due to their broad application prospects in the new era of internet of things (IoTs) as distributed power sources and self-powered sensors. Advanced materials are vital components for TENGs, which decide their comprehensive performance and application scenarios, opening up the opportunity to develop efficient TENGs and expand their potential applications. In this review, a systematic and comprehensive overview of the advanced materials for TENGs is presented, including materials classifications, fabrication methods, and the properties required for applications. In particular, the triboelectric, friction, and dielectric performance of advanced materials is focused upon and their roles in designing the TENGs are analyzed. The recent progress of advanced materials used in TENGs for mechanical energy harvesting and self-powered sensors is also summarized. Finally, an overview of the emerging challenges, strategies, and opportunities for research and development of advanced materials for TENGs is provided.

Application of Triboelectric Nanogenerator in Fluid Dynamics Sensing: Past and Future

The triboelectric nanogenerator (TENG) developed by Z. L. Wang's team to harvest random mechanical energy is a promising new energy source for distributed sensing systems in the new era of the internet of things (IoT) and artificial intelligence (AI) for a smart world. TENG has many advantages that make it suitable for a wide range of applications, including energy harvesting, environmental protection, wearable electronics, robotics, and self-powered sensors. Sensing as an important part of TENG applications is gradually expanding, with the in-depth study of TENG sensing in its working principle, material selection, processing technology, system integration, surface treatment, and back-end algorithms by researchers. In industry and academia, fluid dynamics sensing for liquid and air is urgently needed but lacking. In particular, local fluid sensing is difficult and limited to traditional sensors. Fortunately, with advantages for ordinary TENGs and TENGs as fluid dynamics sensors, fluid dynamics sensing can be better realized. Therefore, the paper summarizes the up-to-date work on TENGs as fluid dynamics sensors, discusses the advantages of TENGs as fluid dynamics sensors in-depth, and, most importantly, aims to explore possible new key areas to help guide the future direction of TENG in fluid dynamics sensing by addressing the key challenges.